Canonicalize on unix style paths when following symlinks
Canonicalize on unix style paths when following symlinks

Many bosh-agent tests rely on this as the paths are made
Windows-specific later.

[#160117030](https://www.pivotaltracker.com/story/show/160117030)

Co-authored-by: Christopher Brown <eb0819782e2e967e3d4f4d71eab0c647ed2659cf@pivotal.io>

cloudfoundry/bosh-utils,cloudfoundry/bosh-utils